1. Field of the Invention
The invention relates generally to propeller drive systems for boats which are especially adapted for use in shallow and weed-infested water. More specifically, the invention pertains to a pivotally suspended, variable depth, propeller drive system for boats, employing a stern tunnel within the floor of the boat, housing a propeller drive sub-assembly.
2. Description of the Prior Art
The prior art teaches a variety of different approaches for powering water craft in shallow waters. For example, in U.S. Pat. No. 1,473,832, a tunnel housing a propeller mechanism, is hingeably mounted upon the bottom, stern portion of a boat. When a shoe member, mounted below the tunnel housing, encounters an object, the tunnel housing swings upwardly. RE. 24,451, issued to Daniels, shows a swingable boat propulsion and steering unit, for use in shallow waters. In U.S. Pat. No. 4,089,289, granted to Sauder, a propeller drive assembly, including a pair of universal joints, is pivotally mounted and movable through a vertical plane. U.S. Pat. No. 5,791,954, issued to Johnson, Jr. shows a vertically adjustable propeller and rudder drive. A trimmable marine drive apparatus is disclosed in U.S. Pat. No. 6,482,057, granted to Schoell. A fin assembly for use with power boats, is shown in U.S. Pat. No. 4,088,091. U.S. Pat. No. 3,469,558, granted to Puretic, discloses a marine propulsion unit having a longitudinal tunnel surrounding a hollow tube with a drive shaft passing through.
The need exists, however, for a propeller drive system for a boat, which is selectively adjustable to a predetermined operational depth;
The need further exists for a propeller drive system having a electric actuator system for selectively determining the propeller""s operational depth;
The need also exists for a propeller drive system for a boat which dynamically and automatically adjusts under forward motion of the boat, to an optimum operational depth for the propeller;
The need also exists for propeller drive system which is pivotally suspended to avoid damage to the propeller in the event the drive system encounters an underwater object;
The need also exists for a propeller drive system which includes a damper in the safety pivoting mounting system to dampen vertical excursions of the drive system;
The need also exists for a propeller drive system using either an air cooled or a self-contained water cooled inboard engine, to eliminate an engine cooling system which is susceptible to mud and weed clogging.
These and other objects will be described below in the drawings and the detailed description of the preferred embodiment to follow.
An inboard propeller drive system for shallow draft boats. The system includes a stern tunnel in the floor of the boat and a propeller drive sub-assembly having its forward end pivotally suspended within the stern tunnel. The stern tunnel protrudes upwardly from the boat""s floor, and includes side walls, a forward end wall, and an upper cover. The bottom portion of the tunnel has an upwardly and rearwardly inclined bottom plate, having a gradual S-shaped configuration. The rear end portion of the tunnel is open, for rearward discharge of the propeller""s wash. A tunnel hood extends rearwardly from the rear end of the stern tunnel.
The propeller drive sub-assembly includes a drive shaft housing. A drive shaft extends entirely through the housing, having a forward end connected to a constant velocity joint and a rearward end upon which a propeller is mounted. A deflector skag is located on the lowermost portion of the drive shaft housing, immediately beneath the propeller. The sub-assembly also includes a cavitation plate mounted to the drive shaft housing, and extending above the propeller. Lastly, a steering mechanism is mounted on the rearmost portion of the cavitation plate. The steering mechanism includes a rudder positioned rearwardly from the propeller, and a lever arm interposed between the rudder support shaft and the steering linkage of the boat.
An intermediate portion of the drive shaft housing passes through an elongated slot in the bottom plate of the stern tunnel. The slot is sized and configured to accommodate upward and downward excursions of the drive shaft housing through a vertical plane.
An inboard air cooled or self-contained water cooled engine is provided forwardly from the forward end wall of the stern tunnel The engine includes a rearwardly directed output shaft which passes through the end wall and interconnects to the universal joint and the drive shaft.
The forward end of the sub-assembly includes a suspension yoke, having a support shaft and a control shaft. Both shafts extend laterally to respective bearings on opposing inner walls of the tunnel, thereby pivotally suspending the sub-assembly within the stern tunnel.
The yoke control shaft passes through its bearing to the exterior of the tunnel. A sprocket is located on the exterior end of the control shaft. A chain has one end encircled around a portion of the sprocket. The other end of the chain is connected to the translatable shaft of an electric screw-drive actuator. When the shaft of the actuator is withdrawn, the sprocket and control shaft are rotated counter-clockwise, raising the propeller. When the shaft of the actuator is extended, gravity rotates the propeller drive sub-assembly downwardly, thereby lowering the propeller. In this manner, with the boat at rest, the depth of the propeller in the water may be may be pre-determined by the user to suit the operational conditions.
Normally, the propeller drive sub-assembly is maintained in a lowered position when the boat is at rest. However, with the boat underway and gaining speed, hydraulic forces from water flowing upwardly through the stern tunnel impress upward forces upon the cavitation plate. The propeller drive subassembly thereby pivots upwardly to an extent determined by the speed of the boat. A limit stop within the tunnel hood prevents the sub-assembly from raising higher than a pre-determined limit.
In the event that the deflector skag encounters either the bottom or an object on the bottom, the upward forces which are generated will pivot the entire sub-assembly upwardly. Once the obstacle has passed, the sub-assembly will pivot downwardly under gravity to its pre-determined depth. A pneumatic or hydraulic damper extends between the sprocket and the tunnel sidewall, to dampen the harshness of vertical excursions of the sub-assembly.